The invention generally relates to composite electrolytes that possess a unique combination of electrochemical and mechanical properties, along with electrodes.
Research in polymer electrolytes for use in rechargeable lithium and lithium-ion batteries has been ongoing for decades. However, performance of conventional electrolytes is still less than desirable. A long-standing goal of electrolyte research generally relates to the preparation of an electrolyte that combines the solid-like characteristics of conventional thermoplastics with the ionic conductivity of low molar mass liquids. It is also desirable that the lithium ion transference number be as close to unity as possible in order to minimize or eliminate electrolyte polarization thereby reducing potential losses and improving power output.
The majority of polymer electrolyte research has focused on employing polyethylene oxide (PEO) and PEO derivatives complexed with various lithium salts. A lithium salt dissolved in a high-molecular weight PEO by itself typically does not yield a room temperature conductivity sufficiently high enough for practical application in a lithium battery (i.e., greater than 10xe2x88x923 S/cm). Various approaches have been attempted to develop solid electrolytes for lithium cells, which yield improved room temperature conductivity. Fauteux et al. [Electrochimica Acta, 1995, 40, 2185] has categorized these approaches into two classes, namely (1) xe2x80x9cpurexe2x80x9d solid polymer electrolyte systems, and (2) network or gel-polymer electrolyte systems, and Koksbang et al. [Solid State Ionics, 1989, 36, 320] has compiled examples of each class. In the first class, blends of polyethers that may be copolymerized with co-monomers can be used to lower the glass transition temperature Tg and produce a polymer with reduced crystallinity. The class also includes co-polymers of polyether-grafted polyether, polysiloxane, or polyphosphazene backbones. Alternatively, plasticizers may be added to the PEO, either as an absorbed liquid or a plasticizing lithium salt, to attempt to effect an increase in conductivity.
U.S. Pat. No. 5,965,299 to Khan et al. proposes a composite electrolyte comprising (a) a surface modified fumed silica filler comprising polymerizable groups being bonded to each other such that the surface modified fumed silica filler is crosslinked in a three-dimensional structure, (b) a dissociable lithium salt, and (c) a bulk medium containing the surface modified fumed silica filler and the dissociable lithium salt.
Notwithstanding the above efforts, there remains a need in the art for electrolytes for use in electrochemical cells including lithium and lithium-ion batteries, which exhibit high conductivities and good mechanical properties. In particular, there is a need for electrolytes that exhibit lithium-ion transference numbers that are close or equal to unity.
In one aspect, the invention provides a composite electrolyte. The composite electrolyte comprises an inorganic clay material and a dielectric solution having a dielectric constant ranging from about 50 to about 85. The composite electrolyte has an ion transference number ranging from about 0.80 to about 1.00.
In another aspect, the invention provides an electrode for use in a battery or electrochemical cell, said electrode comprising a component selected from the group consisting of an inorganic clay filler, a polymer, and mixtures thereof.
These and other aspects of the invention are disclosed in greater detail herein.